The purpose of this study was to assess the accuracy of Duplex scanning in detecting renovascular disease and to compare it with angiography, renal scintigraphy and captopril test for plasma renin activity and isotopic renography. A Duplex scan was performed in 92 renal arteries (46 patients) and compared to angiography. Three degrees of stenoses were established: 0-60%, 61-99% and occlusion. The peak systolic velocity (PSV) in the renal artery and its ratio to the peak velocity in the aorta (RAR) were used to discriminate stenoses > 60%. PSV in the interlobar arteries was used to assess the relative perfusion of both parenchyma. Angiography demonstrated a stenoses > 60% in 23 hypertensive patients. In all of the patients, plasma renin activity was measured and isotopic renograms (pre- and post-captopril) obtained in order to discriminate hypertension of vascular origin. A PSV in the renal artery > 210 cm/s and a RAR > 3.5 were found to be the diagnostic criteria with the best sensitivity and specificity in detecting stenoses > 60%. Based on these data, Duplex correctly identified 49/54 stenoses > 60%; 28/33 stenoses < 60%; and 5/5 occlusions (kappa 0.79). Sensitivity and specificity in detecting stenoses > 60% were 89.5 and 90.7%, respectively. The ratio between PSV in the interlobar arteries of both parenchyma accurately predicted the relative perfusion (ratio between DTPA uptake in both kidneys) in the isotopic test (n = 23, r = 0.91, p = 0.001). The captopril test (for plasma renin activity and isotopic renography) was positive in only five patients.(ABSTRACT TRUNCATED AT 250 WORDS)